1. Field of the Invention
The invention relates to sized glass fibres intended for reinforcing organic materials of the polymer type, in order to obtain so-called composite materials having enhanced mechanical properties.
The invention also relates to the sizing compositions used to coat the said fibres, to the process for manufacturing the composites, and to the composites thus obtained.
In a known manner, reinforcing glass fibres are manufactured from molten glass threads flowing through die orifices, these threads being drawn mechanically in the form of continuous filaments. These filaments are coated with an sizing composition usually in aqueous solution, by passage over sizing members of the coating roll type, before being assembled, torsion-free, as base fibres, which are then collected, in particular by winding on a rotating support.
The use of sizing compositions is made necessary for various reasons: firstly, at the stage of manufacturing reinforcing fibres, the sizing serves as lubricant, protecting the fibres from the abrasion that results from them rubbing against various collecting, winding, etc. members at high speed.
In addition, especially once the sizing has dried, polymerized and/or crosslinked, it provides the fibres with a certain amount of cohesion and makes them hold together by creating inter-filament bonds, thereby avoiding untimely breakage of the fibres and facilitating their handling.
Secondly, at the stage of manufacturing the composite material, sizing enhances the wetting/impregnation of the fibres by the polymer matrix to be reinforced--which is referred to hereinbelow as the "resin"--by helping to create fibre/matrix bonds. The mechanical properties of the final composite material and its resistance to osmosis depend, in particular, on the quality of the fibre/matrix adhesion and the wetting or impregnation capacity.
It is thus seen that in order to assume all of these roles, the formulations of sizing compositions for reinforcing glass fibres are very complex to develop since they must take account of many manufacturing parameters and will depend especially on the type of fibre to be coated, on the type of polymer used for the resin of the composite and, lastly and above all, on the actual mode of manufacture of the composite.
The invention relates particularly to sizing for reinforcing fibres which are incorporated into thermosetting-type polymer matrices such as those belonging to the polyester and/or epoxide family in order to manufacture composite articles by processes known as "open cast processes", that is to say processes by simple moulding, without a counter-mould, which have the advantage of being able to produce, for low investment costs, prototypes, one-off articles or short-run articles, with great freedom in the choice of the shape and the size of the articles.
The invention relates more particularly to sizing for open cast processes known as "moulding by simultaneous spraying", in which the material is deposited in the mould by means of a spray gun which cuts the glass and sprays it onto the mould at the same time as the resin. The operation is usually completed by running a splined roller over it, this smoothing the surface and ironing out any bubbles. Optional attractive of a layer of pure resin, or "gel-coat", to the mould makes it possible to obtain a finished face of attractive appearance.
Although moulding by simultaneous spraying is relatively simple to carry out, it requires that the glass fibres, and most particularly their sizing, have properties that are highly specific to this technique, and these properties may appear to be relatively incompatible with each other.
It is important for the fibres to stay held together after cutting and not to "filamentize" until the end of the spraying against the mould. In addition, it is important for the spraying of the cut fibres to be carried out in a well-dispersed manner, in order for them to form a "carpet" of very uniform density and thickness against the mould.
It is also necessary to obtain impregnation of the reinforcing fibres by the resin which is both rapid and complete, since there is no separate step here of mixing by blending between resin and reinforcing fibres. The sizing should thus aid this impregnation, by being very chemically compatible with the resin in order to establish the fibre/resin bonds.
But from another standpoint, it is just as necessary for the resin/reinforcing fibre mixture to "hold" well to a vertical wall once the spraying has been carried out, both before and after the smoothing operation with the roller, that is to say that there should be no sagging of the mixture or of the resin which tends to accumulate in the lowest part of the open mould.
It is thus also important for this mixture to be sufficiently rigid, with a reinforcing fibre "network" which can hold the resin in place against the surface of the mould, which rather tends towards sizing which is less "compatible" and less "soluble" in the resin.
2. Description of the Related Art
A compromise therefore needs to be found in order for the sizing formulation to be suitable. Thus, sizing suited to this type of moulding is known from patent FR-2,279,688, which uses an aqueous mixture based on polyvinyl acetate, a lubricant, chromic methacrylate chloride and gamma(ethylenediamine)-propyldimethoxysilane. With only one bonding film-forming agent made of polyvinyl acetate, it would seem that the compromise can operate only at the expense either of the rate of impregnation or of the holding, without it being possible to optimize these two properties at the same time.